1. Field of the Invention
This invention relates to a method for preparing a catalyst composition which is used to produce a mixture of lower aliphatic alcohols. The mixture of lower aliphatic alcohols so produced is characterized by containing a substantial proportion of alcohols having from 2 to 6 carbon atoms.
2. Description of Background Art
Lower aliphatic alcohols have been proposed as fuel extenders or as replacements for gasoline for fueling internal combustion engines. Their value as gasoline additives for octane enhancement has also been recognized. Additionally, lower aliphatic alcohols exhibit great commercial potential as commodity chemicals and are excellent cosolvents for methanol in an alcohol/gasoline blend. Certain mixtures of lower aliphatic alcohols have the EPA approval for use and are currently being marketed in the United States. The lower aliphatic alcohols can be produced from domestically available non-petroleum sources and their use in fuels would serve to lessen the dependence of the nation on imported petroleum and petroleum products.
Hydrogen and carbon monoxide, or a synthesis gas mixture of hydrogen and carbon monoxide, can be reacted to form lower aliphatic alcohols. The synthesis gas feed stream can be produced from non-petroleum sources, such as coal, biomass or other hydrocarbonaceous materials. The synthesis gas mixture itself is produced in a partial oxidation reaction of the hydrocarbonaceous materials in commercially available processes, such as coal gasification.
Numerous catalysts and catalytic processes have been studied in attempts to provide a viable process for the production of aliphatic alcohols from synthesis gas or from a mixture of hydrogen and carbon monoxide. Heretofore, the emphasis has been primarily directed to the production of methanol. In contrast, the present invention is directed to a process for making a catalyst composition which is used for producing an alcohol mixture containing a substantial amount of aliphatic alcohols having from 2 to 6 carbon atoms.
Catalysts which are selective for alcohol synthesis, especially methanol or a mixture of lower aliphatic alcohols, are typically prepared via a precipitation or coprecipitation technique. As reported in Nunan, J. et al., "Promotion of Methanol Synthesis over Cu/ZnO Catalysts by Doping with Caesium", J. CHEM. SOC., CHEM. COMMUN., p. 193 (1986), in most instances the nitrate salts are dissolved in water and are precipitated by the addition of a carbonate or hydroxide base. As a result, a hydroxy carbonate or hydrous oxide precursor is formed which is thereafter calcined to the corresponding metal oxide. U.S. Pat. Nos. 4,507,403 and 4,522,938 each describe a method for producing a methanol catalyst via coprecipitation. Similarly, U.S. Pat. Nos. 4,440,668 and 4,562,174 describe catalysts which are also prepared by a coprecipitation technique.
One of the shortcomings associated with the known processes of preparing a catalyst composition by precipitation or coprecipitation includes the difficulty of reproducing the technique so that substantially similar products can be provided. Also, the cumbersome equipment used in preparing the catalyst composition and the lack of control one has over the metal concentrations and the physical relationship of the various metals with respect to each other are other difficulties which have heretofore been encountered.
A process for producing lower aliphatic alcohols from a mixture of carbon monoxide and hydrogen is described in U.S. Pat. No. 4,096,164. The process includes reacting hydrogen and carbon monoxide in the presence of a solid catalyst comprising rhodium with molybdenum or tungsten to produce two carbon atom oxygenated hydrocarbons in which ethanol is the major component. This disclosure is incorporated herein by reference.
U.S. Pat. No. 4,380,589 describes a Fischer-Tropsch process for producing hydrocarbons with improved selectivity to C.sub.2 -C.sub.4 olefins by contacting hydrogen and carbon monoxide with a catalyst including molybdenum, a promoter comprising an alkali or alkaline earth metal and a binder comprising an iron-containing calcium aluminate cement.
U.S. Pat. No. 4,607,055 describes a process for producing lower aliphatic alcohols from a mixture of carbon monoxide and hydrogen in the presence of a catalyst comprising molybdenum; a metal from the group consisting of cobalt, iron and nickel; and silver. The catalyst is modified by the addition of a promoter from the class consisting of potassium, cesium and rubidium. This disclosure is incorporated herein by reference.
U.S. Pat. No. 4,661,525 describes a process for producing lower aliphatic alcohols from a mixture of carbon monoxide and hydrogen in the presence of a catalyst comprising molybdenum and a metal selected from the group consisting of cobalt, iron and nickel which has been promoted by an alkali metal selected from the group consisting of potassum, cesium and rubidium. This disclosure is incorporated herein by reference.
European Patent Application No. 119609 describes a process for producing alcohols from synthesis gas using a catalyst which includes molybdenum with tungsten, rhenium and an alkali metal. This disclosure is incorporated herein by reference. European Patent No. 79132 describes a similar process in which the catalyst contains rhenium, molybdenum and potassium.
Co-assigned application Ser. No. 939,392 filed on Dec. 12, 1986, now abandoned, is directed to a process for producing lower aliphatic alcohols from a mixture of carbon monoxide and hydrogen in the presence of a catalyst comprising rhodium, molybdenum and an alkali metal. This disclosure is incorporated herein by reference.
Previous catalytic processes have been notably effective for converting carbon monoxide and hydrogen feedstocks into hydrocarbons or methanol, but none have been particularly effective for providing a substantial yield of a lower aliphatic alcohol mixture having from 2 to 6 carbon atoms along with the coproduced methanol. It is the present method for preparing the catalyst which produces a catalyst that exhibits favorable productivity and selectivity for the aforestated mixture of lower aliphatic alcohols and, further, which overcomes those shortcomings identified above.